1. Field of the Invention
The invention of the instant application relates to an excitation system for generating a fast pulsed high-voltage discharge to a load, particularly for exciting a high-power laser by an arc-less capacitor discharge as homogeneously as possible, the system having a laser chamber with a gas space wherein at least two laser electrodes are disposed opposite and spaced from one another, the electrodes extending parallel to an optical axis of the laser chamber; a high voltage supply unit; and a pulse-forming network connectible on the input side to the high-voltage supply unit and connected on the output side to the laser electrodes, and having serially connected first and second stripline capacitors connected in parallel with an electrode path of the laser, as well as series and shunt inductances.
2. Description of the Prior Art
Such an excitation system is know from German Published Non-Prosecuted Application (DE-OS) No. 29 32 781. TE-lasers (TE=transversely excited) preferably used in this connection have achieved particular importance because of their high peak powers and large pulse energies. In such lasers, the laser gas which is at high pressure (50 mbar to several bar) as compared to longitudinally excited gas lasers is excited by a homogeneous electrical discharge at several kV via two extended electrodes which are disposed opposite one another and parallel to the optical axis (the direction of emission of the laser). Regarding further details, reference is made to the aforecited German Published Application.
Suitable preionization devices for the excitation system of the foregoing general type are described particularly in German Published Non-Prosecuted Applications (DE-OS) No. 30 35 730 and (DE-OS) No. 30 35 702. It is assumed herein that excitation systems of the foregoing general type are equipped with preionization devices; for this reason, it is not necessary to show them within the scope of the present application.
The excitation system of the type defined at the outset hereto relates, as mentioned, preferably to TE-lasers, for example, to CO.sub.2 -lasers or eximer lasers which represent light sources which, as indicated hereinbefore, are being used in numerous technical applications because of the high efficiency and large output energy per pulse thereof. In these pulse systems efforts are made to switch electric energies in the order of one kilojoule at repetition rates of approximately one kHz in fractions of a microsecond. Spark gaps and thyratrons are used as switches for high voltages and large currents with the short switching times required for the aforementioned laser systems. To date, technical constructions of these switching elements which meet the specified strict requirements simultaneously with long life have not yet become known.
Even since the beginning of the fifties, switching elements which are constructed from saturable inductors have become known from radar technology (Melville: "The use of Saturable Reactors as Discharge Devices for Pulse Generators", Proceedings IEE, London 1951, Vol. 98, Part 3, Pages 185-207). The saturable reactors are used to switch large currents with high current rates of rise. They have purely metallic current conduction which is not subject to the wear and mechanisms such as occur in spark gaps and thyratrons. The use of saturable magnetic reactors therefore has advantages in technical applications wherein long life is required.
The manufacture, composition and properties of the ferro-magnetic core material for such reactors ("metallic glass") is reported, for example, in the journal "SCIENTIFIC AMERICAN", April 1980, pages 84 to 96; reference may also be made to U.S. Pat. No. 4,275,317.
From the aforementioned U.S. Pat. No. 4,275,317, it is known to employ saturable reactors in a special pulse-forming network which is suited for exciting TE-lasers. As will be explained hereinafter in greater detail with reference FIGS. 1 and 2, it is a disadvantage in this pulse-forming network that the entire laser current and therefore, the entire energy converted in the laser must flow through the saturable reactor connected in series with the laser chamber, the saturable reactor retaining, in the saturated state, particularly at large electric energies to be switched, an especially large residual inductance. This residual inductance considerably increases the impedance of the laser discharge circuit as compared to such a circuit which is constructed only from the laser chamber and the charging capacitor. A large impedance is found to be detrimental to an effective excitation of the laser gas.